Conventionally, a technique of performing distribution by unicast communication or multicast communication has been used as a method for distributing the same contents such as contents data (for example, a program file) to a lot of client apparatuses at the same time.
In the case of performing unicast distribution, a communication path is provided between a contents distribution apparatus and each client apparatus. Therefore, as the number of client apparatuses which perform downloading increases, the number of communication paths near the contents distribution apparatus increases, and the download time is lengthened.
On the other hand, in the case of performing multicast distribution, there may be a case where loss of data is caused and complete reconfiguration of contents on a the client side cannot be ensured. For example, when a client apparatus in a low-speed area is receiving contents, loss of a packet occurs in the client apparatus in the low-speed area if data is distributed at a speed exceeding the speed of the area of the client apparatus.
Therefore, in order to avoid the loss problem caused by multicast distribution, client apparatuses detect loss of a packet and, if a client apparatus detects loss of a packet, the client apparatus specifies a packet to be retransmitted, to the contents distribution apparatus. For example, Japanese Patent Laid-Open No. 10-257001 discloses a technique in which a contents distribution apparatus to which a packet to be retransmitted has been specified retransmits the specified packet immediately.